NWS Area Forecast Discussion

FXUS61 KLWX 180145

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
945 PM EDT Tue Jul 17 2018

A cold front will cross the area this evening. High pressure
will return for Wednesday and Thursday before moving offshore
Friday. Low pressure may impact the area during the weekend.


As of 0130 UTC, an area of showers and thunderstorms is moving
east-southeast in an axis that stretches from Carrol to
Montgomery and then to northern Fauquier counties. Some of these
reached severe thunderstorm criteria in the last two hours,
however not too confident that they will be able to maintain it.
Gusty winds and heavy rain are still possible.

Near term guidance suggests that these showers and thunderstorms
will dissipate in the next hour or two as they reach the Baltimore-
Washington metro areas. As the cold front moves across this
evening, a drier air mass will build in with high pressure. Dry
conditions are expected tonight and into early tomorrow with
gusty winds possible.


High pressure will be sliding from the Great Lakes toward New
England Wednesday into Thursday, providing sunny skies, low
humidity, and temperatures a pinch below normal.


High pressure will move off the New England coastline on Friday,
leaving us with southeasterly flow at the surface. This
southeasterly flow should allow some moisture return at the surface,
with dewpoints climbing back into the 60s by day`s end. The majority
of the region is expected to stay dry, but some showers and
thunderstorms may be possible over far western portions of the
forecast area as ascent out ahead of a deep trough approaching from
the Upper Midwest begins to overspread the area.

The aforementioned trough will dig southeastward and approach the
region this weekend. As it approaches, the trough will become
largely cutoff from stronger westerly flow to the north. This will
slow the eastward progression of the system, as it transitions into
more of an upper low. Model guidance is also suggesting that a weak
coastal low may develop off the North Carolina coast, along the a
stalled out frontal boundary (the remnants of the front passing
through our area currently). The coastal low is then picked up by
the larger scale upper-level trough and tracks to the north along
the Atlantic Seaboard. The interaction between the weak coastal low
and the larger-scale trough will be a complex one, so confidence in
the finer scale details is low at this point. Regardless, with the
upper trough slowly approaching, it appears as though showers and
thunderstorms are a good bet both days this weekend. Currently it
looks like both the highest chances for precip, and the highest
areal coverage of storms will be on Sunday.

The majority of model guidance keeps the trough overhead on Monday
as it begins to weaken and shear out. As a result, showers and
thunderstorms will be possible once again on Monday. With the active
weather around, temperatures should run at least slightly below
normal Saturday through Monday.


A few showers and thunderstorms still remain in the area,
expecting them to affect DCA, MTN and BWI in the next hour if
they keep themselves together. IAD may still see shower as well.
After these storms move away or dissipate, and over the other
terminals, expecting VFR conditions with some possible gusty
winds tonight into early tomorrow.

VFR conditions are expected Wednesday through Friday with high
pressure in control. Conditions may deteriorate to sub-VFR this
weekend as a system approaches from the west. Thunderstorms will
be possible each afternoon Saturday through Monday.


A few showers and thunderstorms still remain in the area, which
could bring additional local gusts. A Small Craft Advisory in
effect for all waters tonight. A lull in the winds is observed this
evening as a cold front crosses the waters. Northwest flow will
improve mixing tonight, which will remain favorable into
Wednesday morning. Advisory will remain in effect until 11 am.
There will be room to adjust the ending time if needed.

High pressure will build across the waters Wednesday afternoon,
and continue through Friday. Winds will be 10 kt or less through
this period, from northeast veering southeast.

Low end SCA winds may be possible Saturday through Monday as a
system approaches from the west. Thunderstorms will be possible each
afternoon Saturday through Monday.


MARINE...Small Craft Advisory until 11 AM EDT Wednesday for ANZ530>543.



NWS LWX Office Area Forecast Discussion